This invention pertains to components used with test equipment for sensing, collecting and analyzing physical parameters associated with a conveyor oven. More particularly, the invention pertains to an apparatus and method for simplifying the connection of wires from temperature sensors and/or for providing additional oven profiling information, such as ambient air temperature and heat flow.
Conveyor ovens (also called furnaces) are used in a variety of industries including the electronics, baking, and painting industries. Generally, conveyor ovens have multiple heating zones through which products pass. The heating zones are thermally isolated from each other by air curtains or other means. Such thermal isolation allows each zone to be maintained at a temperature that differs from other zones in the oven. A particular advantage of conveyor ovens with multiple heating zones is that the products can be heated to different temperatures at different times as they pass through the oven. In all industries that use conveyor ovens, it is important that the ovens behave consistently over time. However, after extended use, the ovens tend to change in performance. Some causes of this change include dust accumulating on oven blowers and/or process bib-products, such as fluxes, accumulating on blowers or blocking exhaust ports.
In the electronics industry, conveyor ovens are used to mount integrated circuits and other electronic components to printed circuit boards (PCBs). The multiple heat zones allow the oven to control changes in temperature to prevent thermal stress to the components on the PCB and to meet temperature profile requirements for the flux/paste. Prior to running it through the oven, solder paste is placed on the PCB at predetermined points where components are to be mounted. As the PCB passes through the heat zones, the solder melts, bonding the components to the PCB. Conventionally, prior to a production run, a large number of test PCBs (also called test boards) of the same type were passed through the oven under different heating conditions to ensure the temperature profile of the oven matched the requirements of the components and flux. Each PCB was analyzed after its pass and the best setting for the oven was determined based on this analysis. This test process resulted in a significant number of test boards being scrapped due to improper heating or overuse. Other industries using conveyor ovens have experienced similar problems in setting the ovens for a production run.
To better determine optimal temperature settings and maintain existing or known settings without the need for multiple test boards, electronic data loggers (also called data collectors or monitors) have been developed that attach to a test PCB. One such data logger, the M.O.L.E.(copyright) temperature profiler, is an oven profiler sold commercially by Electronic Controls design, Inc., of Milwaukie, Oreg. Beyond the M.O.L.E., the test PCB has various thermocouples strategically placed thereon. Traditionally, each thermocouple is connected directly to the electronic data logger. The electronic data logger is physically spaced apart from the PCB so as not to absorb heat in the vicinity of the PCB that can result in inaccurate temperature profiling. The data logger stores temperature information provided from the thermocouples, which information can be processed to determine and control the optimal temperature profile of the oven.
This method of collecting data, however, results in multiple connections between the data logger and the thermocouples that can make handling the combined logger/test board apparatus unwieldy. For example, each thermocouple is associated with a dissimilar wire pair connected to the data logger. A typical application may have 6 or more wire pairs extending between the data logger and a PCB containing the thermocouples. The long length and large number of wires often results in the wires becoming tangled and/or unmanageable. Additionally, it is difficult to determine which wire is connected to which sensor increasing the chance for a connection error. The wires may also dangle and catch on the oven as they pass therethrough.
An object of the invention, therefore, is to provide an apparatus to better manage the connection of sensors to a data logger. A further object is to gather and analyze reliable parameters relating to oven temperature and efficiency.
The present invention is directed to a sensor link that attaches to a test PCB used for profiling a conveyor oven. The sensor link is positioned intermediate the thermocouples on the test board and the data logger and functions to organize and shorten the thermocouple wires.
In one aspect, the link has multiple input ports for connecting to multiple temperature sensors (e.g., thermocouples). The link connects the multiple input ports to a single cable for easy attachment to a container housing a data logger. The link may also include other temperature sensors, such as a mass sensor of known weight and/or one or more ambient temperature sensors. The data lines from these additional sensors are also integrated into the single cable for transferring data to the data logger. The data logger stores the temperature information obtained from the sensor link. The temperature information may be downloaded from the data logger to a computer for further profiling analysis of the conveyor oven.
The test board has multiple temperature sensors strategically placed on its surface for temperature analysis. Typically, each temperature sensor is associated with a pair of signal conductors. The signal conductors from the temperature sensors are removably coupled to input ports on the sensor link by a plug/receptacle combination. The sensor link has internal wiring to route temperature information from the signal conductors to the single cable.
A container houses the data logger and provides a thermal barrier to protect the data logger from the extreme heat of the oven. The container has an input port for receiving the cable from the sensor link and acts as an adapter to electrically couple the cable to the data logger (data loggers typically have multiple input ports and cannot connect to a single cable). Specifically, the container divides and directs the multiple conductors in the cable to corresponding multiple output portsxe2x80x94typically, one output port for each temperature sensor. The output ports of the container mate with the data logger so that the two can be plugged together. Thus, the data logger is electrically coupled through the container, cable, and sensor link to the temperature sensors. For data loggers designed to receive a cable that provides data from multiple temperature sensors, the output ports on the container are not needed as the cable can directly plug into the data logger.
In another aspect, the sensor link physically attaches to the test PCB and is integrated with a container that houses the data logger. The sensor link may still have a single cable that extends from the sensor link to the container. In such a case, the sensor link may be removably attachable to the container. When the sensor link is attached to the container, the single cable is folded into a cavity on the container. When the sensor link is detached from the container, the sensor link is attached to the test PCB and the container is spaced apart from the test PCB, so as not to absorb heat and affect temperature profiling information associated with the test PCB. Alternatively, the sensor link may be integrated with the container and have multiple conductors passing the thermocouple information to the container so that the single cable is not used.
Whether or not a single cable is used, the sensor link may include one or more additional sensors to provide further profiling information. For example, the sensor link may include a metal mass of known weight. A temperature sensor is positioned on the surface of or within the metal mass for sensing the temperature of the metal mass. Temperature information obtained from this temperature sensor is hardwired to the output port of the sensor link so that such temperature information may be routed to the data logger. An ambient temperature sensor may also be included on the sensor link and hardwired to the output port in a similar fashion.
In yet another aspect of the invention, a position sensor mounted to the sensor link senses position of the sensor link within the oven. For example, a reed switch may be actuated when the sensor link passes a magnet or magnets mounted to the oven. Thus, accurate position data and conveyor speed can be calculated.
Accordingly, the present invention provides a sensor link for easily transferring signals from two or more temperature sensors located on a test board to a data logger so that the data signals can be used to analyze conveyor oven performance. The sensor link is attachable and detachable from the test board so that it can be reused on multiple test boards and in different conveyor oven environments.
Various advantages and features of novelty that characterize the invention are particularized in the claims forming a part hereof. However, for a better understanding of the invention and its advantages, refer to the drawings and the accompanying description in which there are illustrated embodiments of the invention.